1. Field of the Invention
The present invention is related to a method for surface cleaning or treatment of semiconductors, glass, or resins, and device for producing electrically charged water as utility water for the above methods, more particularly a technique for providing an electrolysis cell, which can produce electrically charged water suitable for surface cleaning or treatment without using chemical in consideration of environmental protection. The electrically charged water produced by using the electrolysis cell also has antimicrobial activates, and is suitable for cleaning and sterilizing medical devices for which high cleanliness is required.
2. Description of the Related Art
Electrolysis cell using ion exchange membrane, as shown FIG. 1, facilitates the electrolysis of water with low conductivity such as RO water treated using a reverse osmosis membrane pure water, and ultra pure water. In this cell, a fluorinated cation exchange membrane 5 is usually used.
And then an anode electrode 4 in the anode cell 1 and a cathode electrode 9 in the cathode cell 6 are closely attached to the membrane 5. The notation 2 denotes the anode chamber inlet, 3 denotes anode chamber outlet, 7 denotes the cathode chamber inlet, and 8 denotes the cathode chamber outlet.
The ion exchange group in fluorinated cation exchange membrane 5 shown in FIG. 1 is known to enhance the dissociation even in the pure water according to the reaction (1).—SO3H→—SO3−+H+  (1)
The dissociated hydrogen ions increase the electro conductivity of pure water, which contains no impurities, and then decrease the electrolysis voltage.
Next, the reaction (2) and (3) proceed when pure water is electrolyzed using the cell shown in FIG. 1.
At anode2H2O→2H++O2+2e−  (2)
At cathode2H++2e−→H2  (3)
These reactions increase the oxygen concentration in the anode solution and the hydrogen concentration in the cathode solution, while leaving the essential properties of electrolytic water unchanged.
In other words, the charged water produced using electrolysis cell shown in FIG. 1 may not be suitable for the surface cleaning or treatment of semiconductors, glass, or resins.
In order to enhance the cleaning or surface treatment efficacy, anode water is required to be more oxidative and/or acidic and cathode water is required to be more reductive and/or alkaline. However, the electrolysis cell shown in FIG. 1 is difficult to produce the effective solutions.
For example, the oxidation and reduction potential (hereinafter abbreviated as ORP) of anode water is from 200 to 300 mV (vs., Ag/AgCl) and pH is around neutral: the ORP of normal pure water is around 200 mV.
The three-chamber cell shown in FIG. 2 is designed to solve the problem mentioned above, where the middle chamber 111 is added between the anode chamber 11 and the cathode chamber. 16. Using the three-chamber cell easily electrolyzes pure water or ultra pure water.
Referring to FIG. 2, the three-chamber cell has the chamber 11 and 111 separated by the ion exchange membrane 151, chamber 16 and 111 separated by the ion exchange membrane 152, the middle chamber 111 filled with ion exchange resins as a solid electrolyte, the middle chamber inlet 112 and outlet 113, cathode 19 and anode 14 provided in such a way to be closely attached to the ion exchange membrane 151 and 152, respectively, the anode camber inlet 12 and outlet 13, and the cathode chamber inlet 15 and 17.
The three-chamber cell has the following merits. Reductive species such as dissolved hydrogen gas produced in the cathode chamber 16 are likely to migrate into the anode chamber 11 though the ion exchange membrane 5 when the cell depicted in FIG. 1 is used. However, the middle chamber 111 in the three-chamber cell control the diffusion of reductive species from the cathode chamber 16 to the anode chamber 11 and then the more strongly oxidative anode water can be obtained. In the cell shown in FIG. 2, migration of hydrogen ions formed on the anode 14 toward the cathode 19 is limited, and then the electrolysis reaction (4) takes place in addition to the reaction (3):H2O+2e−→½H2+OH−  (4)
This reaction suggests that the pH of cathode water tends to shift to the alkaline region.
In another viewpoint, these phenomena suggest that hydrogen ions formed in the anode chamber 11 in the reaction (1) remain partly in that chamber.
In the three-chamber cell shown in FIG. 2 the anode solution, therefore, is likely to be charged with the hydrogen ions, whiles the cathode water is charged with hydroxide ions.
Electrochemical analytical methods are suitable for monitoring charges or the like to experimentally confirm the phenomena mentioned above. For example, the changes in measured values can be monitored by a pH sensor equipped with a glass electrode or ORP sensor which measure the oxidation-reduction potential of platinum electrode surface as a standard of a silver/silver chloride electrode. These sensors, following potential changes in the electrodes as the index, are suitable for confirming charges of electrolytic water. A temperature of the electrolytic water is usually kept at from 18 to 24° C. during measurement (the temperature in the following examples was kept at the almost same levels).